Polymerization of butadiene hydrocarbons in the presence of an arylalkyl selenol



PQLYMERIZATION on BUTADIENEHYDROCAR- BONS IN THE PRESENCE OFAN 'ARYLALKYL snLENor Bailey Bennett, Columbus, Ohio, assignonby mesne assignmeuts, to the United States of America as represented by the Secretary of the Army N Drawing. Application February 25,1954, SerialNo. 412,626

Claims. (Cl. 260-823) This invention relates to the polymerization of butadiene hydrocarbons and mixtures of butadiene hydrocarbons with copolymerizable vinyl compounds in aqueous emulsion in the presence of selenol compounds.

ln'the past it has been the practice to use mercaptans as modifiers in elastomer formation. This process is illustrated, for example, by the disclosure in'U. '8. Patent No. 2,281,613 to Wollthan et a1. However, such .prior art processes using mercaptans have certain well-known 'disadvantages, as enumerated below, which'the present invention is intended to overcome.

There is disclosed and claimed in copending application Serial No. 342,715, filed March 16, 1953, now US. Patent 2,737,507, a process and a new compositionof matter produced by the polymerization of butadiene hydrocarbons and mixtures of butadiene hydrocarbons with copolymerizable vinyl compounds in aqueous emulsion in the presence of aliphatic selenol compounds. This invention relates to the use of arylalkyl selenol compounds "for the same purpose.

A disadvantage of the mercaptans is that the mercaptans were developed for use in emulsion polymerization systems at 50 C. If it is desired to carry out emulsion polymerizations at high temperatures, such as up'to 150 C., the mercaptans are not well adapted for use'asmo'difiers. The activity of mercaptans is relatively great at high polymerization temperatures, with the imercaptan being consumed too rapidly to satisfactorily'modify and regulate the elastomer polymerization. v

Another disadvantage of the mercapt'ans' is' 'alackof control over the formation rate of the elastomers at high polymerization temperatures.

Still another disadvantage is that an oil-resistantela'sto mer polymerized in the presence ofamercaptanat low temperature when compounded into a rubberlikeimaterial would not exhibit the optimum balance of oil-resistance and low-temperature properties. For example,'it is well known in the art that if the rubberlikematerial should have a high oil resistance, the low-temperature properties would be poor; on the other hand, if the low-temperature properties were good, the oil resistance of the compounded rubber would be poor.

Still another disadvantage is that the mercaptans'are not satisfactory for use in continuous polymerization processes carried out at high temperatures. vAsatisfactory continuous polymerization process requiresrapid'conven' sion'to the elastomer, with proper modification thereof, and a modifier that will remain active :for the duration of the continuous polymerization,process. *Mercapta'ns are too reactive at the higher temperature'and overmodify the polymer. Furthenmercaptansare tooirapidly consumed at high temperatures and thus the reaction will: die out if the amount of mereaptan used islessenedsomas to avoid overmodificat-ion of thepolymer.

Therefore, it is anobject ofthisinventionltoprovide a new and useful method :of modifying 'or"regulati-'ng ice Still another object of the invention is to provide a method of control over the formation of synthetic elastomers at high polymerization temperatures.

Another object of the invention is to provide a synthetic oil-resistant elastomer that, when compounded into a rubberlike materialwill exhibit the optimum balance of oil-resistance and low-temperature properties.

Another object of this invention is to provide a synthetic elastomer which contains selenium as an integral part thereof.

Still another object of the invention is to provide .a method of continuous high-temperature polymerization. In the practice of this invention, modifier action is possible at the high temperature required for thesuccessful operation of. a continuous polymerizationprocess.

Other objects and advantages of the present invention will be apparent in view of the following detailed disclosure and description thereof.

.'The present invention relates to the process, andthe product produced thereby, of polymerizing a material selected from the group consisting of 1,3-butadienelhydrocarbons and mixtures of 1,3-butadiene hydrocarbons with copolymerizable compounds having a single C=C double linkage in aqueous emulsion in the presence of selenols of thearylalkyl'type, having at least two carbon'atoms in the alkyl group.

The arylalkyl-selenols are those'compounds containing at least two and not more than 16 carbon atoms inthe alkyl group,'and can be expressed by the followinggeneral formula:

where n is any'integer between 1 and 17.

The selenols behave in a manner similar to that of mercaptans in emulsion polymerization but with reduced activity at any given polymerization temperature. I The following examples are submitted for the-purpose of illustrating the present invention and are not to be construed as limiting or restricting it thereto. In all examples the proportions are given in parts by weight.

EXAMPLE I A copolymer of butadiene-acrylonitrile was obtained at a polymerization temperature of 120 C. Will'lifl polymerization time of 4.0hours by the addition to parts "of'water of 10 parts of soap (1 & G SF flakes manufactured by Procter and Gamble, Cincinnati,"0hi o)',' 0.6 parts of potassium chlorideand 0.1 parts of potassium persulfate; to the aqueous "phasewere added 35 parts of acrylonitrile, 4 parts of phenyl ethyl 'seien'ol, and 55 parts of butadiene. Chemical analysis of the'elastorner produced thereby indicated 2.8 percent elemental selenium as integral part thereof.

EXAMPLE II A copolymero-f'butadiene-acrylonitrile was obtained in the same manner as Example I, except that the modifier was phenyl propyl selenol, 4 parts, and the polymerization time was 2.0 hours.

EXAMPLE iii A copolymer of butadiene-acrylonitrile was obtained in the same manner. as Example 1, except that the modifier was phenyl butyl selcnol, v2 parts, and the polymerization time was'ZLShours.

EXAMPLE IV A'copolymer-of but'adiene-styrene was obtained f-ata polymerizationtemperature of 120 C. withiapolyrneri z'ation time of"4.0"hou rs-'by the addition to'l'SOpa'fts'. f. waterofdfi'parts o-f'soap' (P '& G SF'fi'akes manufactured by Procter and Gamble, Cincinnati, Ohio), 0.6 parts of potassium chloride and 0.1 parts of potassium persulfate;

to the aqueous phase were added 25 parts of styrene, 4 parts of phenyl ethyl selenol, and 75 parts of butadiene.

EXAMPLE V A copolymer of butadiene-acrylonitrile was obtained at a polymerization temperature of 90 C. with a polymerization time of 4.0 hours by the addition to 180 parts of water of 3 parts of soap (P & G SF flakes manufactured by Procter and Gamble, Cincinnati, Ohio), 0.6 parts of potassium chloride, and 0.002 parts of potassium persulfate; to the aqueous phase were added 35 parts of acrylonitrile, 2 parts of phenyl ethyl selenol, and 65 parts of butadiene.

EXAMPLE VI Copolymers obtained by Example I were compounded into a rubberlike material in a standard test recipe consisting of 100 parts of copolymer, 4() parts of carbon black (Statex B, distributed by the Binney and Smith Company, New York City, New York), 5 parts zinc oxide, 1.25 parts sulfur, and 1.75 parts of rubber accelerator (Altax, manufactured by the R. T. Vanderbilt Company, New York City, New York).

The use of arylalkyl selenols is particularly adapted to polymerization at relatively high temperatures where the usual modifying agents, the mercaptans, are consumed very rapidly. The lower order of activity of the selenols makes them particularly well adapted for use at high temperatures.

Another advantage is that the reduced activity at higher temperatures of the selenols enables elastomers of superior properties to be obtained as, for example, the favorable balance of oil-resistance and low-temperature properties of a butadiene-acrylonitrile copolymer.

Table 1 illustrates that a butadiene-acrylonitrile copolymer produced by the practice of this invention will exhibit a slight decrease in the conversion of monomers to copolymers, but also a significant decrease in gel content as the amount of selenol present is increased with time and temperature remaining constant. The data set forth in Table I were obtained withelastomers prepared as per Example I except that the selenol was varied from 0 to 4 parts, by weight.

Table I Parts by Weight of Phenyl Ethyl Seleuol Conversion,

Gel Content, Percent Percent These data indicate the desirability of using arylalkyl selenols for high temperature polymerization because of the modifier or regulator activity which may be obtained by the use thereof.

High temperature emulsion polymerization is desirable and advantageous in certain instances, as, for example, enhancing certain properties of the elastomer so prepared. Of particular importance are the properties of oil-resistant, rubberlike materials relating to the balance of oil-resistance and low-temperature properties. By carrying out the emulsion polymerization in the presence of the selenols disclosed herein, an oil-resistant elastomer may be obtained, which, when compounded, will show very favorable oil-resistance properties and at the same time have extremely good low-temperature properties. In the prior art utilizing mercaptans at low polymerization temperatures, it was necessary to sacrifice one property to obtain the other. By high-temperature polymerization in the presence of the selenols disclosed herein,

both the oil-resistance properties and low-temperature properties of the elastomer will be extremely favorable with little or no sacrifice of one property to obtain the other.

In the experimental production of butadiene-acrylonitrile el-astomers, polymerized in the presence of an arylalkyl selenol, it is evident that the favorable balance of oil-resistance and low-temperature properties of such elastomers is promoted by the increase in polymerization temperature. The synthetic elastomers prepared by the new processes have been shown to be superior in the balance of oil-resistance and low-temperature properties to that of similar elastomers which have been prepared with mercaptans.

This favorable balance of properties in butadieneacrylonitrile type elastomers is possible, due solely to the use of selenols disclosed herein and elastomer modification obtained thereby.

To illustrate this new, novel, and surprising balance of oil-resistance and low-temperature properties, a test was made on elastomers prepared in Example I and compounded into a rubberlike material as per Example VI.

(1) Oil-resistance properties (expressed in terms of percent swell on twenty-four hour immersion in reference fuel No. 2). Selenol-modified elastomer, 73.1 percent.

(2) TR-70 low-temperature properties (expressed as the percent retraction at a particular temperature, that is, the temperature at which 70 percent retraction is obtained). The TR-7O value indicates serviceability of an elastomer after long exposure to low temperature.

selenol-modified elastomer, minus 26 C.

Thus, it may be readily seen that an arylalkyl selenolmodified elastomer, when compounded into a rubberlike material, presents a favorable balance of oil-resistance and low-temperature properties.

A further advantage is that the arylalkyl selenols possess regulator or modifier activity, a property which makes them available for the continuous rapid production of synthetic elastomers at high temperatures in emulsion systems. Such regulator or modifier activity may be obtained bythe use of selenols at emulsion polymerization temperatures in excess of 120 C. This property would enable this polymerization system to be used in the continuous high-temperature polymerization process such as might be carried out in a tube or pipe through which emulsions flow continuously. In such a process, rapid conversion coupled with good modification would be desirable. The materials necessary for obtaining such activity, of necessity have to possess modifier or regulator activity.

While the particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects and, therefore, the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention. Further, it is understood that the invention is not to be limited to the specific form, or compositions, or temperatures herein described and shown.

What is claimed is:

1. The process which comprises polymerizing a material selected from the group consisting of 1,3-butadiene hydrocarbons and mixtures of 1,3-butadiene hydrocarbons with copolyrnerizable compounds having a single C=C linkage, in aqueous emulsion at a temperature of at least C. in the presence of phenyl alkyl selenols having at least two but not more than 16 carbon atoms in the alkyl group.

2. The process according to claim 1 wherein the copolyrnerizable compound is acrylonitrile.

3. The process according to claim 1 wherein the copolyrnerizable compound is styrene.

4. The process according to claim 1 wherein the selenol is a phenyl ethyl selenol.

5. The process according to claim 1 wherein the selenol is phenyl propyl selenol.

6. The process of polymerizing a 1,3-butadiene hydrocarbon in emulsion in water with an emulsifying agent, a polymerizing initiator, a comonomer and a phenyl alkyl selenol having at least two but not more than 16 carbon atoms in the alkyl group, wherein the polymerization is carried out at a temperature of at least 90 C.

7. The process according to claim 6 wherein the comonomer is acrylonitrile.

8. The process according to claim 6 wherein the comonomer is styrene.

9. The process which comprises polymerizing a material selected from the group consisting of 1,3-butadiene hydrocarbon and mixtures of 1,3-butadiene hydrocarbons with copolymerizable compounds having a single C=C linkage in aqueous emulsion at a temperature of from C. to C. in the presence of a phenyl alkyl selenol having at least two but not more than 16 carbon atoms in the alkyl group.

10. The process of polymerizing a 1,3-butadiene hydrocarbon in emulsion in water with an emulsifying agent, a polymerizing initiator, a comonomer and a phenyl alkyl seleuol having at least two but not more than 16 carbon atoms in the alkyl group, wherein the polymerization is carried out at a temperature of from about 90 C. to about 150 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,281,613 Wollthan et a] May 5, 1942 

1. THE PROCESS WHICH COMPRISES POLYMERIZING A MATERIAL SELECTED FROM THE GROUP CONSISTING OF 1,3-BUTADIENE HYDROCARBONS AND MIXTURES OF 1,3-BUTADIENE HYDROCARBONS WITH COPOLYMERIZABLE COMPOUNDS HAVING A SINGLE C=C LINKAGE, IN AQUEOUS EMULSION AT A TEMPERATURE OF AT LEAST 90*C. IN THE PERSENCE OF PHENYL ALKYL SELENOLS HAVING AT LEAST TWO BUT NOT MORE THAN 16 CARBON ATOMS IN THE ALKYL GROUP. 